Thermosensitive recording materials express image parts and non-image parts as differences in temperature distribution, and various systems have been devised such as melt transfer or sublimation transfer of coloring agents, coloring reaction between two components by heat melting or capsule disruption and alteration of optical characteristics by phase transition. Since such types of thermal recording media can produce record images by a simple dry system and also have an advantage of being maintenance-free, they are broadly used as output materials such as of various printers, word processors and facsimiles. In addition, with the progress in the development of laser recording apparatuses, their application to optical disks and plate making materials has been examined in recent years.
Though silver halide light-sensitive materials which require wet treatments have been generally used as the plate making materials, several techniques have been proposed in recent years regarding the thermosensitive recording system because of the increasing demand for the development of a dry process in order to simplify the treating steps and resolve the environmental pollution problem caused by the treated liquids. Among these techniques, a laser-aided image recording system is desirable from the viewpoint of resolution; for example, a high output laser-aided system which is called dye ablation has been developed, and its recording materials have been disclosed for example in JP-A-7-164755 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), JP-A-7-149063 and JP-A-7-149065, and its image forming apparatuses for example in JP-A-8-48053 and JP-A-8-72400.
In this system, image recording is carried out by a method in which a recording material having a dye composition comprising an image dye coated on a base, a substance having absorption in the laser wavelength region (infrared absorbing substance) and a binder is irradiated with laser from the dye layer side. The energy generated by the laser causes a rapid local change in the image forming layer at a spot where the material is exposed to the laser beam and thereby puts out the substance from the layer. According to the aforementioned references, this is not a completely physical change (e.g., melting, evaporation or sublimation) but a certain chemical change (e.g., bond breakage) and is not partial elimination of the image dye but its complete elimination. Such a dye ablation system has problems in that high output laser is essential for the improvement of dye-elimination efficiency at the region exposed to laser and it is necessary to employ a dust catcher in juxtaposition with the system in order to collect the eliminated dye.
As a system which does not require a dust catcher, a description about an ablation transfer type image recording method which uses laser as a heat source is disclosed in U.S. Pat. No. 5,171,650. This system uses a dye donor sheet containing a dynamic separation layer on which an ablative carrier topcoat is finished, and the image is transferred to an adjacent acceptor sheet aligned with the donor sheet. Thus, it has a problem in that the discarded sheet after image recording becomes a waste material. Also in this case, high output laser is essential for improving transfer efficiency. Accordingly, the related art thermosensitive recording systems in which laser ablation is used have problems in that high output laser is essential and discharge of dust and waste materials is unavoidable.
On the other hand, a system in which a so-called "Dry Silver" system is further developed is described in JP-A-6-194781 as a thermosensitive recording system which does not accompany laser ablation. In this system, recording is carried out with laser on a recording material which contains a thermally reducible silver source, a silver ion reducing agent and a light-heat conversion dye, but its practical performance is not sufficient in terms of the shell life of non-image parts and heat sensitivity.
Also, regarding other laser-aided thermosensitive recording systems, compounds whose absorption changes by thermal decomposition of carbamate are described in U.S. Pat. No. 4,602,263 and U.S. Pat. No. 4,826,976, and a compound which develops yellow color by thermal decomposition of t-butoxycarbonyl group introduced into hydroxyl group is described in U.S. Pat. No. 5,243,052. Since these systems use irreversible monomolecular reactions, they are suited for extremely short-time laser-aided image recording, but their sensitivity is not sufficient so that further improvement of the sensitivity is expected.
In addition, no practical idea has been proposed on a laser-aided heat mode system as a method for the formation of UV mask image (360 nm to 420 nm; corresponding to the exposure light source on PS plate) to be subjected to plate making material use.